Yes, I have lots of theory. And also 30 years real world hot rodding experience, 15 years racing and 20 years as an industrial chemist. But if you believe you can get more power from running higher octane fuel than the engine requires, then buy it and enjoy your extra horsepower. I really don't care either way. The placebo effect can be very strong.

While you're at it. Have a word with the big 3 in Detroit, you've got some information they would pay you very well to obtain - it's something they've spent countless hours (years) working on but obviously got wrong. Also the 1st law of thermodynamics, you'll need to set a few people straight on that one as well.

.... And back well into the 90s, the first mod Mustangers did was to bump the timing on the Windsors. It gained 5-10hp on the dyno, and shaved tenths off their 1/4mile. There was no premium involved. The rodders simply removed the factory "safety factor" and got their timing closer to optimum. Everybody now knows the timing advance on the earlier EFI 5.0 was very conservative (ie. original engine system did not have an optimised spark advance curve)

"In summary. Any given engine will make maximum power from the lowest octane fuel that still allows an optimum spark advance curve"

And if you dont run premium after bumping the timing it pings, thats the reality.

Better tell all these trip computers to snap out of that Placebo effect!

mine is doing the same sort of thing dead stock ef xr8 only really fill half a tank at a time i only get about 150 to 170 klms

o2 sensors

Wrong again. An EB-ED 5.0 can take an extra 2-4 degrees on regular 91 petrol without any detonation. Been there, done it many times, no problems whatsoever, nets a few stray horses as noted. But these are the only Aussie falcon models that you can directly compare to the earlier 5.0 Mustangs like you did above, same engine with (for all intent and purpose) an identical EEC program. EF and onwards V8's had a very different EEC program, and a slightly different engine

But if it makes you feel better to use higher octane, go right ahead. The oil companies love that sort of thing.

i think the question has been lost. It was directed at fuel consumption not output. Ultimately higher octane fuels in modern engines will achieve better economy due to the slower burn rate. Lower octane fuels burn off more quickly causing exhaust oxygen levels to lean, and ecu reacts in turn increase injector rate allowing more fuel to be burn, thus using more fuel. With the slower burn fuel in high octane fuels and exhauast gases are able to be scavenged for longer.

However XA is right in some respects. This application is on relevent in motors that are able to utilise the slower burn rate. Some motors dont have the combustion efficency to allow all the fuel to be burn causing excess unburnt fuel to enter the exhaust system, and effectively having the opposite effect to above. Oxy sensor detects the excess fuel as motor running to rich and ecu leans of injector rate.

Which will effectively improve economy on the short but eventually the continued result of unburnt fuels fouls components in a way that correct rich/lean mixture cant be detected by oxy sensor. Thus richening fuel levels constantly

So yes in certain applications such as low hp early model EFI cars the recommended manufacturer RON is preferable but in the more modern higher Hp EFI and high Hp cars in general. higher octane fuels while only minor Hp gains may be found, definate fuel economy gains will be found

But in the applications of High Hp cars, withour doubt there are performance upgrades of using higher Octane. eg methonol, aviation fuels as used in champ cars, drag cars. top fuel.

Note: Not always true it depends on application. Eg. F1 cars use a very similar blend of fuel to the highest octane fuel that can be bought at the bowser.

Food for thought, or in this case, petroleum for go-go

Hey guys - I'm pretty novice when it comes to cars (I change the oil make sure everything looks OK... that's about it). Basically I just got a 6cyl XH and sold the old EL. I was getting about 400-500 ks a tank in the EL, and the XH (which has a bit more on the clock) I'm getting about 260 a tank! I do a mix of highway and city, but admittedly mostly city at the moment.

I checked and found out that the fuel tanks are the same size, they weigh about the same...

Read on here that I should check/replace the oxygen sensors - can anyone give me a heads up on doing this? I don't even know where it is (I'm guessing on the thermostat?). Is it possible to check/clean this? If so how?

Don't have a multimeter/voltometer ... but can get my hands on one and then have no idea what to do with it...

I'm thinking a 6cyl doesn't have a MAP so I don't need to go there right?

I'll get stuck to the timing etc (well... a mechanic will) if I don't see any improvement from the sensor change/check.

I'll learn one day...

Thanks.

The 6 cyl does have MAP.